1. Technical Field
The present application relates generally to an electrophotographic imaging device and more particularly to a fuser for an electrophotographic imaging device.
2. Description of the Related Art
In the electrophotographic (EP) imaging process used in printers, copiers and the like, a photosensitive member, such as a photoconductive drum or belt, is uniformly charged over an outer surface. An electrostatic latent image is formed by selectively exposing the uniformly charged surface of the photosensitive member. Toner particles are applied to the electrostatic latent image and thereafter the toner image is transferred to the media intended to receive the image. The toner is fixed to the media by a combination of heat and pressure applied by a fuser.
The fuser may include a belt fuser that includes a fusing belt and an opposing backup member, such as a backup roll. The belt and the backup member form a nip therebetween. The media with the toner image is moved through the nip to fuse the toner to the media. Belt fusers allow for “instant-on” fusing where the fuser has a relatively short warm up time thereby reducing electricity consumption. Fusing speed is a function of the width of the fuser nip and the belt surface temperature, among other things. A fuser with a relatively wide nip is able to fuse toner to media moving at higher speeds through the nip than a comparable fuser with a relatively narrow nip. Further, a fuser with a higher belt surface temperature is able to fuse toner to the media faster than a fuser with a lower belt surface temperature. Higher fusing speeds in turn lead to higher print speeds.
Conventional ceramic and inductive heating belt fusers utilize a stationary pressure member to form a flat nip with a backup member. Ceramic and inductive heating belt fusers typically include high temperature grease disposed between the contact surface of the belt and the pressure member to reduce the friction therebetween. FIG. 1 shows a prior art belt fuser with a ceramic heater. A stationary pressure member 7, a ceramic heater 5 and a heater housing (not shown) are positioned inside an endless fusing belt 3. The stationary pressure member 7 forces the endless fusing belt 3 to contact a pressure roll 9 to form a fuser nip 2. FIG. 2 shows a prior art belt fuser with an inductive heater. A stationary pressure member 15, an inductive heater 13 and a heater housing (not shown) are positioned inside an endless fusing belt 11. The stationary pressure member 15 forces the endless fusing belt 11 to contact a pressure roll 19 to form a fuser nip 4. The fuser nips of the ceramic and inductive heating belt fusers can generally be expanded to form a wider nip but unless the set point of the heat source is increased, widening the nip does not significantly raise the surface temperature of the belt, which is necessary for high speed fusing, because the belt is only heated within a predefined region. However, in some instances, increasing the set point of the heat source can cause degradation of grease between the contact surface of the belt and the stationary pressure member. Grease degradation drastically increases the likelihood of belt stalls in the fuser as a result of increased friction wear. Further, the ceramic heater is coupled to the stationary pressure member thereby requiring a flat nip.
Lamp heating belt fusers utilize a rotating quartz tube pressure member to form a rounded nip shape against a backup roll. FIG. 3 shows a known lamp heating belt fuser. A rotating quartz tube pressure member 20 and a lamp 22 are positioned inside an endless fusing belt 24. The rotating pressure member 20 forces the fusing belt 24 to contact a pressure roll 26 to form a fuser nip 28. Lamp heating belt fusers are capable of achieving higher belt temperatures than ceramic or inductive heating belt fusers because the rotating quartz tube pressure member allows radiant heat emitted from the lamp to be delivered to substantially the entire inner surface of the belt. However, the rounded nip makes it difficult to increase the width of the fuser nip because it requires increasing the diameter of the quartz tube and the fusing belt. This, in turn, leads to more thermal mass in the system and increases the warm-up time of the fuser. Further, the rotating quartz tube pressure member requires a rounded nip due to its circular cross-section.
Accordingly, it will be appreciated that an efficient belt fuser with enhanced fusing performance is desired.